Refractory concrete



Patented Aug. 1, 1950 CROSS REFEFZEt-LCE BEFRAUIORY CONCRETE .Frank .E.:Lobaugh, South Plainiield, N. 1., as-

signor to Universal Atlas Cement Company, a corporation of Indianadioinrawing. application September 17, 1946, Serial No. 697,574

:4" f "zfllaims. (cues-s4) L G ll'his invention relates to an improvedrefractory, .more particularlya refractor concrete or .whichan essentialcomponent is calcium alumiessesn .imoug the objects of the invention .isthe provision of an improved reiractory composition yielding articlessuch as refractory .shapes 1'01 improved strength at elevatedtemperatures. and of refractory shapes resulting .from such composition.A turther obiectnl .the invention is the provision of .an improvedrefractory composition .ior .use in the forming of veneer or washcoatings of improved strength and refractory properties, and orrefractory .shapes provided with such coatings.

.. Refractory materials or concretes composed .of calcium aluminatecement and various retracrtoiy aggregates have been employedsuccessfully in applications where they are subjected to hightemperatures. Such applications include roofs, side walls, and hearthsof various types of furnaces, coke oven door'linings, and annealingturnace and tunnel kiln car tops. Calcium alumi- ;nate cement when mixedwith water form cer- 'tain hydrated compounds which, when heated toelevated temperatures, lose appreciable portions of the combined waterwhich results in reduced hydraulic strength. "This loss of combinedwater increases with increase in "temperature until at some temperatureabove 1600' F. all combined water is driven off and no hydraulicstrength is present. when calcium aluminate cement is used as 'abinderfor-refractory aggregates the resulting concrete likewise loses itshydraulic strength upon heating to some temperature above 1600" F. Attemperatures in the vicinity of 'l600 TL, however, the concrete developsan appreciable ceramic strength by reason of the melting of some oi. thelow melting compounds in the cement which combine with the aggregate toform a ceramic bond. Such ceramic strength increases with the increasein temperaturenntil the softening-point or the concretemixtureis'reached.

A The 'improved refractory composition n! the 45 present inventionincludes 'as 'an admixture :an element or elements which :are at leastsubstantially insoluble iin water and in cement mixes, and thus 'do notnflect the hydraulic strength 'of the concrete, -but which have arelatively low meltingpointythatis, 1600 F. or :below, so that atsuchtemperatures they provide .the refractory concrete with -a ceramic bond10: increased a p a;

50 Calcium aluminate cement 2 strength. Such admixture 'must have asolubilityin waterand in cement mixes not exceeding 0.1% by weight thus.not appreciablyaltering the time of hydraulic set of the concrete orits 5 strength, but must .melt "at a low enough temperature to addmaterially to the strength of the :ceramic bond .at temperatures whichsubstanbtlally overlap the upper end of the temperature range at whichhydraulic strength is present in the concrete. Specifically, theinvention emd dys for such purpose a rit which is a smelted rraw minimof luble i.o s.qiutle.;inezselliq materials. Such smelting is carriedout by meltifitfis'oluble materials in the presence ofsumcientsilicaafiddfalhlg'h enough temperature to dorm kiibstantially insolubl e silicates. The :Irits employed in the present invention musthave suilicient silica present so that upon being melted they formsubstantially insoluble siligo oatesjince otherwise they might affectthe hydraulic set of the cement and thus defeat the purpose oi. theadmixture. Frits, both glaze and porcelain enamel. which have a meltingpoint of 1600" F. -or less-and which have solugs bilities in water-andin-cement mixtures not .ex-

-eeeding 0.1% by weight of the irit, may be :em-

ployed in the practice or the invention.

The present invention consists in the addition of such frit "to calciumaluminate cement in the formation of re rac ry ma rial. e rac- 3otory-material'within the scope of the present invention consists ofcalcium aluminate cement, the above defined Hit, and refracto materialswhich may be inthe iorm of aggregates. The refractory concrete or thepresent invention is 5 made from a mix, the constituents of which liewithin the following limits, given as per cent 01' the'total weight ofthe mix:

v Per cent Calcium aluminate cement 5 to 60 4 Refractory aggregate 15 to93.5

Substantially insoluble frit melting at 1600 F. or less 0.5 to

In certain (instances it .is preferred to use :a somewhat higher .low.limit of the hit content. In such cases the constituents of the mix liewithin the iollowinglimits, given as per centoi the total weight of themix orbatch: a

Per cent Ste Refractory aggregate 15to92.5 Simstantially insoluble :iritmelting at 1600" F. or less 3.517025 FEE NO. 1

Per cent S102 22-56 A1203 3*- 8 B20: 843 K20 3- '7 NazO 3-14 Minoramounts, totaling approximately 20% at most of CaFz, NazCOa, NaNOa, CaO,Fezoa, MgO, and so forth.

The above frit is suitable for use as a porcelain enamel ground coat.

FRIT NO. 2

Per cent S10: 9-73 A1203 2-10 B203 5-28 K 2- 9 NazO 2-16 Minor amounts,totaling approximately at most of NazCOs, NaaAlFe, NaNOa, CaO, FezOa,h5g0, and so forth.

Frit No. 2 is suitable for use as a porcelain enamel cover coat.

FRIT NO. 3

Per cent 8102 31-62 B203 12-25 F8203 1- B (29.0 5-20 NazO 5-24 Minoramounts, totaling approximately 10% at most, of CaO, FezOs, MgO, and soforth.

Frit No. 3 was formed by smelting together a mixture of Rasorite, aborax compound, Calox NazO, CaCOa, and SiOz to yield a composition withe above range. Rasorite contains approximately 27.50% NazO, 61.50%13203, and 5.50% S102 with lesser amounts of A1203, F8203, CaO, and MgO.Calox consists of calcined The constituen s of the mix are suppliedthereto in either united or granular form to allow them to be uniformlydistributed throughout the mix and consequently the resulting concrete.Those consituents which form the bond are preferably finely ground tofaciliate their reaction. The calcium aluminate cement, for example, maybe of such fineness that practically all particles will pass through a100 mesh screen, and the frit may be of approximately the same particlesize. The refractory aggregate or filler, which may be cla grog, crushedfirebrick, e anded shale, diatomaceous earth, vermiculite, crushed redBrick, and the like, or combination of such aggregates, may be of anydesired particle size or range of particle sizes consistent withsubstantial uniformity of distribution throughout the resultingconcrete.

The mix may conveniently be made by mixing the calcium aluminate cementand the frit in dry condition to a uniform color, the refractoryaggregate being thoroughly wet down with water and then added to thecalcium aluminate cement and fri't mixture. Sufficient water is added tothe resulting mixture to render it workable, the amount added dependingupon the manner in which the mixture is to be subsequently handled inthe formation of the concrete shape or structure. Thus, if the concreteis to be cast into a mold or form, particularly if the shape isintricate, the mix should be of puddling consistency. For simple shapes,so cast, less water may be used, whereas if the mix is to be tamped orvibrated into place or molded under pressure, still less water may beused. It is obvious that sufficient water may be used in all cases todevelop fully the hydraulic strength of the cement and that an excess ofwater should be avoided.

The above directions apply mainly to the formation of cast shapes orstructures from the mix of the invention. When such mix is to beemployed for the making of veneer coatings or wash coats to other morerefractory shapes such as bricks, tiles, and the like, or as coatings orpatches on larger shapes or structures such as furnace walls and kilncar tops, it is obvious that the procedure must be modified accordingly.Thus for the veneer coatings, which ordinarily will be of the thicknesson the order of one inch, the aggregate will be required to be of aparticle size smaller than that for most cast shapes. For the washcoatings all ingredients ofthe mix should be finely ground. Further,when used as f a wash coating larger amounts of water are required thanin the other applications above outlined.

After the castable mixtures above described have been shaped or molded,and in the case of the veneer or wash coating after the refractory shapeor structure has been so coated,such shapes, consisting solely of or inpart of the wet refractory mixture of the invention, are dried and thenheated. Usually for shapes of large section, such as cas furnace walls,the practice follows approximately that employed in the drying andheating of newly constructed flrebrick linings. The concrete may bedried for a period of several days, after which the furnace is heated attemperatures which gradually increase up to operating temperature.Smaller blocks and shapes composed solely of such refractory mixture,such as cast bricks, tiles, and slabs, and refractory shapes with veneeror wash coatings of such mixture, may be kept for a time on the order oftwenty-four hours in a high humidity-constant temperatureatmosphere,dried at a low temperature on the order of 230 F., and then subjected toa high temperature approximating that at which the shape may be used,for example. 1600 F.

Concrete resulting from mixes made in accordance with the presentinvention, after having been dried and heated as above, possessesincreased strength at both atmospheric and elevated temperatures ascompared to similar concretes made from mixes containing no frit. Suchincreased strength of the concrete of the present invention at roomtemperatures are shown by the results set out by the following tables,which give the compressive strengths of two-inch cubes of mixturescontaining the indicated percentages by weight of calcium aluminate"cement, hit, and

of fgmiabove as seen composition, as

CROSS REFERENCE was The trite were around to such fineness thatnot morethan 2.6% remained on a 200 mesh sieve. The calcium aluminate cement wasof such fineness that 14.7% remained on a 325 mesh sieve.

Each oi the values given for each test in the following Tables to-IV',vinclusive, represents the average of test on three similar'two-inchcubes.

TABLE I1 4 Calcium illuminate ggmggt-Ha dite'plus Force ain enamel Zn!Compressive Strength. lfigant In Cent Per Ce nt HPer Q ent pg; iililq.Inch 4 y in n in a e in s 11' g a Wightof To fiatch, match, fifi llitch,y

Cement by wt. by wt. by wt.

1400 F. v 1000 F.

TABLE II;

Galciumaluminate' cement-crushed grebrick plus porcelain enamel jritCompressive Strength, Per-Gent Her Cant Pu'Cent 6%? lbs; per Sq. Inch 4Frit By t in Cement 1n Firebrick in Days Firing etw hug! Batch; Tot?!Batch, mob, by 1400 F. 1aoo F.

0' 0' 20: 7 79;: 1,193 854 123;- 251 20.0 71.5: 1,150 125 1 as 4.2 19.515.1. 1, 029 859 w as 18:7 72.1 1,108 1,372 75- 1:23 17.8 are 1,112 a;953. mu 17.11 17.0 66.0 1,219. 3,914

alcompressive strength test at room temperature by subjecting it togradually increasing pressure until a point of failure oiethe cube wasreached.

In Tables I and 11 below the mixes employed contained calcium aluminatecement, rcelain asamelirit. d, afimegreeatm-Hay tan expanded following.screen analyses:

SCREEN ANALYSES The porcelain enamel frit was one designated No. 1100.Its analysis falls, generally under that ment in the compressivestrength of the concrete,

mte ifiiibiushdiliebrick, respectively. Such refractory 11mm,

As. seen from Table I the addition of as small an amount as 3.7 byweight. of porcelain enamel fritin the total batchresults inmarkedimproveboth when fired for four days at 1400 F. and at 1600 R, suchimprovement in strength increasing as the amount. of frit in. the batchis increased. With a concrete containing crushed firebrickaggregate,TableII, the increase in compressive strength in concretefired for fourdays at 1600 F. is not obtained until at least 4.8% by weight of frit inthe total batch is employed, marked increase in strength being obtainedupon the; use of, still higher percentages of irit. The strenethoi theconcrete shown in Table II.when fireiat. 1400 F. at four. days. remains,substan w tially constant withincreased frit. content.

Increased. strength is also obtained when. glaze hits are employed as anadmixture in men's:

0' used. cement-aggregate mixes.

In the tests on two-inchcubes setout. inTableslII andIV below the mixesemployed. are the same as those in follows: 65 Tables I and It.rispectively, except that inv BORCELAm AME! ERIT Tables III and IV t e.frit employed is a glaze No um frit'having the following composition:

Per. cent.

s10: I 1 .5110 GLAZE FRIT A '12 Per cent B203 12.4 No.20 10.6 CaO 4.3CaO 17.7 NazO 15.6 FezOs 1.1 K20 3.4 B203 23.9 n 6.1 s10, 46.7

EXAMINER itia'sbi 7 It will be seen that such glaze frit falls withinthe composition range of irit No. 3 above.

cl ,1. A mix adapted for making refractory con- TABLE 111 ,Qllsium.aluminatememenh ggggijgglus glaze zit Com naive 8 Per Cent Per Cent PerCent Per Cent lbs per Sq. m Frit By Frit in Cement in Haydite in DaysFiring et- Woight of Total Batch, Total Batch, Total Batch,

Cement by wt. by wt. by wt.

14oo F moo" F TABLE IV Calcium aluminate cement-crushed ,flrebriclc plusglaze frit Compressive Strength Per Cent Per Cent Per Cent 6%;? lbs. pers Inch 4' Frit By Frit in Cement in Firebrick in Days Firing tit- Weightoi Total Batch, Total Batch, Batch Cement by wt. by wt. b wt Y mm 2'.moo r.

0 0 2o. 7 79.3 1,193 854 12% 2. 5 2o. 0 77. 5 1, 663 l, 444 25 4. 8 19.6 75. 7 1, 613 1, 775 50 9. 3 18. 7 72. l l, 665 2, 387 76 13. 3 17.868. 9 2, 919 4, 182 100 17. D 17. 0 66. 0 3, 463 5, 919

strength of the concrete increases with increased frit content.

Although it is not desired to limit the invention to a. particulartheory of operation, it is believed from the observed results that theincreased compressive strengths of cements of the present invention aredue to the fact that the frit functions as a flux, reacting under theheat when the refractory concrete mixture is fired to aid in theformation of the ceramic bond, which by reason of such fiuxing action isstronger and more uniform than that obtained in similar mixtures withoutthe frit. The use of such frit melting at a relatively low temperaturesuch as 1600', F. or below and substantially insoluble in water andcement mixes does not, as explained, aflfect the hydraulic strength ofthe concrete but causes the development of a strong ceramic bond attemperatures which substantially overlap the temperatures at which theconcrete retains substantial hydraulic strength.

Whereas particular embodiments of the invention have been describedabove for purposes of illustration, it will be evident that numerousvariations of details are possible within the teaching of the invention.The scope of the invention therefore is to be defined by the followingclaims.

crete by the addition of water comprising from 5 I to 60% ofcalcium-aluminate cement; from 15 to 93.5% of aggregate selected fromthe group consisting of fire-clay grog, crushed brick, expanded shale,diatomaceous earth and vermiculite; and from .5 to 25% of a trit havinga solubility less than .1% by weight in water-cement mixtures andefiective to form a vitreous bond when heated to a temperature of 1400F., said frit being composed for the most part of from 9 to 73% silicondioxide, from 7 to 38% of oxides of metals selected from the groupconsisting of aluminum and boron and from 4 to 25% of oxides of metalsselected from the group consisting of potassium and sodium.

2. A mix for making refractory concrete, said mix consisting ofcalcium-aluminate cement and from 12.5 to by weight of cement of a frithaving a solubility less than .1% by weight in water-cement mixtures andeffective to form a vitreous bond when heated to a temperature of 1400F., said frit bein composed for the most part 01 Irom 9 to 73% silicondioxide, from 7 to 38% of oxides of metals selected from the groupconsisting of aluminum and boron and from 4 to T 25% of oxides 01'metals selected from the group consisting of potassium and sodium.

'- FRANKELOBAUGH.

i .nnraimnoss crran The following references are of record in the file01111115 WW??? UNrrED STATES PA'I'ENTS number Name Date s'zsasz DaltanFeb. 16, 1926.

1. A MIX ADAPTED FOR MAKING REFRACTORY CONCRETE BY THE ADDITON OF WATER COMPRISING FROM 5 TO 60% OF CALCIUM-ALUMINATE CEMENT; FROM 15 TO 93.5% OF AGGREGATE SELECTED FROM THE GROUP CONSISTING OF FIRE-CLAY GROG, CRUSHED BRICK, EXPANDED SHALE, DIATOMACEOUS EARTH AND VERMICULITE; AND FROM .5 TO 25% OF A FRIT HAVING A SOLUBILITY LESS THAN .1% BY WEIGHT IN WATER-CEMENT MIXTURES AND EFFECTIVE TO FORM A VITREOUS BOND WHEN HEATED TO A TEMPERATURE OF 1400*F., SAID FRIT BEING COMPOSED FOR THE MOST PART OF FROM 9 TO 73% SILICON DIOXIDE, FROM 7 TO 38% OF OXIDES OF METALS SELECTED FROM THE GROUP CONSISTING OF ALUMINUM AND BORON AND FROM 4 TO 25% OF OXIDES OF METALS SELECTED FROM THE GROUP CONSISTING OF POTASSIUM AND SODIUM. 